s2jay

i have a sunoco station nearby that has 100 octane (6.99/gallon), if i use this gas will i notice any gains???. mods are aem cold air, invidia TP+cat-back. experiences???

mikegarrison

You will save weight because your wallet will be lighter.

If you are using the OEM ECU, you will not have any significant performance change.

Ape_X

You'll be less prone to Detonation. So on a hot day out at the track or out for a drive, you can mash the pedal with confidence.

Not that you'll detonate much anyway... Stock ECU retards timing like a MoFo when it senses heat.

ChefJ

Our cars are tuned for 91 octane on the stock ECU. That means even 93 octane is overkill.














Unless you are boosted and have a tune for 100 octane then you can get +- 50-80hp

jzz30

although our cars are designed for 91 octane, do we really get 91 out of the pump? i talked to some guys at a chevron refinery, and they told me that they send the gasoline distribution center 80something octane and they add their own additives to raise the octane. now with E10 the guy told me that they get methanol and calculate what octane it should raise the gasoline to with 10% being in there. and he also told me that they dont actually test the octane number. but this is in hawaii, other places may differ...
moral being it may give a bit more performance if the octane is actually lower than 91. maybe put in 93? but 100 is overkill i think. plus isnt it like $8.XX a gallon? thats like $80-90 bucks to fill!!! unless you drive the car only on the weekends it could add up...

Project22a

Won't make a difference without tuning. And even then, 100 seems pretty high unless you're FI or have some kind of crazy high compression n/a build.

R3DS2K

Every car that suppose to run 91 octane should really have 93.. its not overkill cuz California i think is the only state that has 91 has there highest octane..

93.. will def help since its really suppose to run 93.. i wish i can prove it.. but i read it a long time ago.. and it said that all cars that suppose to take premium should really take 93 oct not 91 but since 91 is the highest it what we use

ChefJ

Thats the issue around here anyway. its either 87,89, or 93 91 isn't even an option. I know that for a fact in Michigan and in Georgia. If you want to cheap out of it you can go 50/50 89 to 93.

I ALWAYS run 93 octane though.

AJS2K!

Unless your boosted or a have a really high compression ratio 100 octane is a waste. It's not going to hurt anything but its not gonna help either. If it leaded definatley stay away from it.

slipstream444

You need to understand what an octane rating is before you can apply it.
http://en.wikipedia.org/wiki/Octane_rating
http://en.wikipedia.org/wiki/Octane
http://en.wikipedia.org/wiki/Gasoline

Here's the reader's digest version to answer your question:
The Octane rating is a measurement of the equivalent content ratio of iso-octane to n-heptane. Pure octane has an octane rating of 100. 87 octane is basically 87% octane and 13% heptane. The octane rating is also affected by the additives in the fuel. This is why there are fuels with octane ratings over 100.
The ratio developed shows the relative stability of the fuel - its resistance to "detonation" or pre-detonation.
High octane fuel is actually more stable than lower octane fuel - and therefore is less likely to detonate prior to the intended fuel ignition. This is beneficial in high compression engines, and forced induction engines (to include nitrous).
The biggest misconception about high octane fuel is that it increases the output of the engine. This isn't the case - directly (just the opposite if the octane number was inflated due to additives like ethanol).
There isn't a higher content of energy available in high octane fuel compared to lower octane fuel. However, high octane fuel allows you to run higher compression and/or forced induction, while lowering the chance of pre-ignition. This means you can cram more air and fuel into every combustion cycle. This also allows your engine to run more advanced timing.
Conversely, if your car's ECU senses detonation (liekly due to low octane) - it pulls the timing way back, which in turn greatly reduces the performance of your engine.

What does this mean to your relatively OEM U.S. spec S2000 (none of your mods would affect the way your car responds to higher octane)?
There's a limit to the benefit from running octane levels above the factory required 91 octane rating. This limitation is based on the max ignition timing advance available via the ecu.
I ran varying mixtures of 101 octane unleaded race gas and 91 octane to determine the point of diminishing returns with higher octane. I did this over about 15,000 miles.
Here's what I found: performance increased up to approximately 94 to 95 octane and leveled off at ~96 octane. Performance actually dropped off above 96 octane (acceleration and mileage). The performance increase above 93 octane was not worth the extra cost of adding the 101 octane - therefore, I ran 93 octane most of the time (when I could find it).
You won't see a benefit running 100 octane over straight 93 octane. In fact you may see a slight decrease in performance. You'll probably see the best performance with a 55% 91 octane to 45% 100 octane mix during the colder months, and 60% 91 octane to 40% 100 octane in the hotter months (due to density altitude change with hotter temps - hot air is less dense).

As mentioned before - NEVER RUN LEADED FUEL.

I hope this info helps.